CZ338795A3 - Process of treating waste water containing soluble phosphates by precipitation procedure - Google Patents

Abstract

This method uses the low dissolubility of the compounds of phosphates with calcareous ions where waste water is mixed with calcium hydroxide and calcium chloride. In the cleaned waste water first of all the pH is modified by calcium hydroxide in an aqueous suspension or in solution in a reactive mixture and then a molar ratio of the elements Ca<2+> and PO4<3-> is set by the solution of calcium chloride. After mixing the extracted precipitate is separated from the aqueous phase by sedimentation. Before terminating the mixing a polymeric organic flocculant is added to the reactive mixture, for example based on polyacrylamide.

Description

Technical field

The present invention relates to a process for purifying waste water heavily contaminated with soluble phosphates in various ionic forms by a precipitation process.

Hitherto stories of __t ec

Waste waters from the chemical industry, containing soluble forms of phosphates, usually have a pH in the region of weakly acidic to weakly basic. In this pH range, phosphates are predominantly present in the form of dihydrogen phosphates and monohydrogen phosphates. For the purification of these waters, precipitation processes are generally used, which utilize the low solubility of some phosphates, such as iron or calcium. In the case of the precipitation of iron phosphates, an excess of precipitating agent is required due to the inactivation of part of the reagent by hydrolysis, and the resulting product has a further use for the presence of iron.

In the case of calcium phosphate precipitation, calcium hydroxide is usually used as a precipitating agent. However, calcium hydroxide, when added, is applied by both components, i.e., Ca ^{&lt; 2 &gt}; When the required amount of Ca ² * ions is added to eliminate the sparingly soluble calcium phosphate, the corresponding OH * ions are in excess, so that precipitation occurs in a strongly alkaline region in which the dissolution of calcium hydroxide is more difficult, which has a negative effect on the entire precipitation process. . The precipitate is predominantly hydroxylapatite, which has a Cas (PO4) 3 (OH) composition with a small proportion of calcium monohydrogen phosphate (CaHPO4) with a proportion of Ca ² * components: P04 ^3- = 1.6: 1. After separation of the precipitate from purified water, adjust the pH by addition of acid prior to discharge into the stream, thereby undesirably increasing the dissolved salt content. In addition, it is more difficult to dissolve calcium hydroxide in the alkaline region, which is negative in the entire precipitation process.

SUMMARY OF THE INVENTION

It has now been found that for the purification of waste water containing soluble phosphates by a precipitation process using low solubility of calcium phosphate compounds with calcium hydroxide and calcium chloride added to the waste water, the present invention is advantageously based on The process of claim 1, wherein calcium hydroxide in an aqueous suspension or solution to adjust the pH of the reaction mixture in the range of 9.9 to 10.5 is added to the purified water, followed by a solution of calcium chloride in such an amount that the molar ratio of Ca components ²⁺ : PO 4 ³ was 1.1 to 1.4 to 1. The reaction mixture was stirred. The precipitate formed is separated from the aqueous phase. Preferably, a solution of a polymeric organic flocculant, such as a polyacrylamide-based substance, is added to the reaction mixture before the mixing is complete.

This method brings a number of advantages over the current state. The precipitation reaction proceeds immediately as it is not hampered by the accompanying processes. The calcium ions entering the reaction are in stoichiometric proportions as in the precipitate formed, so that no excess reagent is required. The pH adjustment in purified water prior to discharge does not require large amounts of acid. The addition of the polymeric organic flocculant at the appropriate time will then cause the formation of larger, well-settling particles.

DETAILED DESCRIPTION OF THE INVENTION

Example 1.

The waste water contains 6.4 mmol / l PO4 ³ - and 0.87 mmol / l Ca ²⁺ at pH 4.35. To one liter of this water was added 8.2 mmol of Ca (OH) 2 in 20.2 mL of a 3% aqueous suspension. The pH of the mixture was 10.47. CaCl 2 in solution (1.4 mmol in 0.3 ml of saturated solution) was added to the mixture. After mixing, the mixture was allowed to settle for 30 minutes and then analyzed according to the following table:

pH

Ca ²⁺

PO ^{3 -} Sludge volume

9.87 mg / L

7.8 mg / 1% v / v

Example 2

The precipitation of Example 1 was repeated except that one minute before the end of stirring, a polyacrylamide-type auxiliary flocculant was added in an amount of 2 mg / L. The resulting sludge volume after

The 30 minute sedimentation was 21% obi.

Example 3

To one liter of the waste water of Example 1 was added 7.3 mmol of Ca (OH in 15 ml of a 3% aqueous suspension. The oH of the mixture was 10.05. CaCl 2 in solution of 2.3 mmol in 0.55 ml of saturated solution was added. After stirring, the mixture was allowed to settle for 30 minutes, the effluent having a pH of 9.78, containing 9.3 mg / l PO4 and a slurry volume of 36% by volume.

Industrial exploitability

The invention finds application in the purification of waste water from the chemical industry containing soluble forms of phosphates.

Claims (2)

PATENTOVÉ Claims Process for the purification of waste water containing soluble phosphates by a precipitation process using a low solubility of calcium phosphate compounds, wherein calcium hydroxide and calcium chloride are added to the waste water, characterized in that calcium hydroxide in aqueous suspension is first added to the purified water or in a solution with a pH adjustment of the reaction mixture of 9.9 to 10.5, and then a solution of calcium chloride in an amount resulting in a molar ratio of Ca ²⁺ : PO ^{4 3} components in the reaction mixture of 1.1 to 1.4 to 1. the mixture is stirred and the precipitate formed is separated from the aqueous phase. 2. A process for the purification of waste water containing soluble phosphates by the precipitation process according to claim 1, characterized in that a solution of a polymeric organic flocculant, for example a polyacrylamide-based substance, is added before the mixing is complete.